Daan Hulsmans

48 Chapter 2 Figure 2 Interaction plot for intervention effects on substance use frequency, substance use severity and binge drinking. Note. Gray bars reflect 95% confidence intervals. Y-axis indices on Graph A and C reflect frequency scores on a five-point scale with categories (1) ‘never’, (2) ‘less than once a month’, (3) ‘every month’, (4) ‘every week’, (5) ‘almost every day’, while Y-axis indices in Graph B reflect the sum score of 10 items with these 5-point scales assessing severity of alcohol (AUDIT) or drug (DUDIT) use. Graph A is the frequency of the substance(s) (alcohol and/or cannabis and/or other drugs) that each adolescent most frequently used at baseline. Graph B reflects the severity each adolescent’s most severely used substance (alcohol or drugs) at baseline. Graph C reflects the frequency with which adolescent consume more than six glasses of alcohol per day. 4. Discussion This study evaluated the effectiveness of Take it Personal!, an indicated prevention program for substance use (alcohol, cannabis, other illicit drugs) in adolescents with a mild intellectual disability. Intervention effects were found for substance use frequency and binge drinking, but not for substance use severity. Results on specific substances reveal a nuance to the null-results on substance use severity. That is, the intervention was effective on the severity of alcohol use, indicating that adolescents whose drug use was most problematic at baseline were able to reduce the severity of alcohol use at 3-month follow-up, but not the severity of drug use. Our results were consistent with the effectiveness studies of personalitytargeted substance use prevention programs for non-disabled adolescents that showed intervention effects for alcohol use frequency (Conrod, 2016), binge drinking (Conrod et al., 2013; Conrod et al., 2006) and cannabis use (Mahu et al., 2015; Newton et al., 2018) over periods of 4–6 months in Great-Britain, Canada and Australia. Moreover, other studies on the severity of use did not find intervention effects on problematic drinking in Dutch and British adolescents (Lammers et al., 2017; Conrod et al., 2006). However, a Canadian study found a significant reduction in symptoms of problematic drinking in the short- (4 months) and long term (24 months) (Conrod et al., 2011). Take it Personal! mainly helped adolescents to decrease the frequency of their alcohol, cannabis or other illicit drug use, but

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